1. Field of the Invention
The present invention relates to an AC switch for connecting or disconnecting modification circuitry into and out of the power section of an ultrasonic generator. AC switching devices such as triacs, relays, silicon controlled rectifiers and/or transistors can be utilized.
2. Discussion of the Related Art
Ultrasonic generators are utilized in a variety of applications including but not limited to cleaning, plastic welding, cell disruption, sonochemistry, degassing, micro machining, and developing photosensitive polymers. This diversity in applications requires a versatile generator or a variety of ultrasonic generators. Frequency adjustment, amplitude control, power changes, waveform shaping, power control and output impedance selection are useful control parameters for ultrasonic generators that are designed for a variety of applications. It is therefore an object of the present invention to make ultrasonic generators more versatile by the switching of resistive, reactive, and active components.
Heretofore, different mechanisms and methods have been utilized to modify the parameters of an ultrasonic generator, like the use of linear amplifiers or drive circuits to accomplish frequency adjustment, amplitude control, power changes, waveform shaping and power control. The desired parameter(s) is formed in a low level analog or digital format and then amplified to the proper power level to drive the ultrasonic transducers. U.S. Pat. No. 5,076,854 is a typical example of this technique. The disadvantages of linear power amplifiers are that they are expensive, inefficient and physically large.
Another technique is to switch off the current to the output of the ultrasonic generator earlier for lower power and lower amplitude. This technique is known in the art to control power output and amplitude output from an ultrasonic generator. This has the disadvantage of switching losses in the semiconductor switching devices. These switching losses increase with increasing frequency, making this method even more disadvantageous as the ultrasonic frequency is increased.
Known devices and methods control of output amplitude by controlling the supply voltage to the ultrasonic generator or oscillator. U.S. Pat. No. 4,736,130 illustrates this method. The output voltage of the voltage regulator is changed as the output amplitude is also changed in the same fashion. A switching regulator can be used as the voltage regulator. Increased size and expense are disadvantages of this approach. Other known methods include the use of a linear regulator to regulate the voltage. The disadvantage of this method is inefficiency and the requirement for excess heat removal.
Other known devices have used AC switches in the output of ultrasonic systems to multiplex different transducers to an ultrasonic receiving and sending circuitry. An example is found in U.S. Pat. No. 6,051,895. This patent shows a series field effect transistor configuration used as the AC switch. Other AC switches, such as those formed from IGBTs, BJTs have been utilized. However, AC switching at the output of ultrasonic systems for the purpose of multiplexing a selected generator to a transducer array or multiplexing of a selected transducer to a generator or receiver suffers from the need for multiple generators or multiple transducers. The present invention can accomplish the same task with a single generator.
Various references demonstrate the versatility and switching abilities of triac switches. U.S. Pat. No. 5,892,314 discloses a triac switch that acts as a gate to an energy storage inductor to transfer the energy in a piezoelectric film to the energy storage inductor. In this patent the triac, however, is the active device in the generator circuit, not an AC switch used to modify the output power, amplitude, frequency or impedance of the generator circuit. U.S. Pat. No. 5,930,946 discloses a pest control device where a triac is used to generate an electromagnetic field in the AC wiring. U.S. Pat. No. 4,023,004 discloses a triac to control the power supply of a microwave oven. U.S. Pat. No. 5,592,073 discloses a circuit for controlling a triac switch. U.S. Pat. No. 5,734,289 describes another, yet different, circuit for controlling a triac switch. U.S. Pat. No. 4,027,226 shows a bipolar inverter that can use triacs as the switching mechanism. Finally, U.S. Pat. No. 4,845,391 discloses a circuit to simulate a triac switch.
In the above-identified patents the mechanisms and methods for changing the parameters of an ultrasonic generator suffer from numerous disadvantages, such as large size, inefficiency, switching losses. It is an object of the present invention to eliminate such shortcomings.
The present invention is directed to the creation of an AC switch by electronic circuitry. The AC switch as presented in this invention will exchange a modifying circuitry (which contains resistive, reactive, and active components) into and out of the power section of an ultrasonic generator. Therefore, the output of the ultrasonic generator will be modified by the modification circuitry disclosed, by way of example, herein. The AC switch is operatively connected to the modification circuitry. It switches the modification circuitry into and out of the output stage of the generator. The control circuitry is associated with the AC switch and is adapted to turn off and turn on the AC switch. The AC switch will swap resistive, reactive and active components and networks of these components into and out of the power section of ultrasonic frequency generators. The present invention provides a simple and reliable manner to increase the number of parameters and diversify the capabilities of an ultrasonic generator.
The AC switch introduces a modification circuit that is able to (1) maintain full power output from a multiple frequency ultrasonic generator as the center frequency of the generator is changed, (2) step sweep the output of an ultrasonic oscillator, and (3) vary the output power and amplitude of a non self-oscillating ultrasonic generator. A fixed frequency oscillator can be modified to accomplish certain of these functions and to sweep frequency. This is accomplished by the step sweeping and successive AC switching in of capacitors and/or inductors (i.e. modification circuitry).
This patent will suggest a number of applications in which the AC switch is created by triacs. A triac is a three terminal semiconductor, which controls current in either direction. The triac is suited to create a simple and less expensive AC switch than the use of transistors. Nevertheless, it will be obvious to those skilled in the art that other circuitry can be substituted for triacs. One example of such other circuitry, which simulates a triac, is one that includes back to back silicon-controlled rectifiers. Also, a series/parallel active device configuration or bi-directional lateral insulated gate bipolar transistor, can act as the AC switch.
The phrase xe2x80x9cmodification circuitryxe2x80x9d as used herein is defined as resistive, reactive and active components and networks of these components. The circuitry will have two main leads and one or more control leads available for active components or networks containing active components. One of ordinary skill in the art will readily appreciate that it is possible to introduce a different value of a resistive or reactive component through the use of a transformer; therefore, in some cases a transformer winding or tap can be the part of the modification circuitry that is switched by the AC switch.
The modification circuitry is placed in parallel with an AC switch when it is required that the modification circuitry be inserted into a conduction line of the ultrasonic generator. The modification circuitry is placed in series with an AC switch when it is required that the modification circuitry be inserted between two nodes of the ultrasonic generator. When connected in series, the modification circuitry is inserted at any time in the cycle by turning on the AC switch. In the case of a parallel connection, the modification circuitry is removed from the generator when the AC switch is on. The reverse effect will happen when the AC switch is turned off. The addition of a control circuitry to the AC switch supplies turn on and off signals to the AC switch. Where the AC switch is a triac, the control circuitry will provide (1) a turn off signal to the ultrasonic generator for a period of time at least as long as the triac turn off time, (2) the turn off signal to the triac for a period of time at least as long as the triac turn off time, and (3) concurrent signals for a period of time at least as long as the triac turn off time. The use of this control circuitry is necessary due to the fact that the speed of triacs is too slow to allow them to go off when conducting an ultrasonic current.
Another embodiment of the invention includes modification circuitry capable of modifying the following parameters of the output of an ultrasonic generator: frequency; amplitude; power; impedance; and waveform. The parameter will change in accordance to the purpose of the application or generator. The modification includes at least one capacitor, one inductor, or one resistor. Finally, it can also include an active/passive network with a control circuitry adapted to control the active components in the network.
In another embodiment of the invention, a control circuitry capable of supplying a turn off signal to the AC switch for a duration D1 is illustrated. If the AC switch is a triac, the control circuitry will also supply a turn off signal D2 to the generator, where D1 and D2 are concurrent for a time equal to or greater than the triac turn off time. The same will apply if the AC switch is comprised of back to back silicon controlled rectifiers. In the case of the modification of the output frequency of an ultrasonic oscillator, the xe2x80x9ccontrollerxe2x80x9d will represent the control circuit. This controller can be further modified to selectively activate or deactivate components so as to step sweep the output frequency of an oscillator.